Surface treatment

ABSTRACT

TREATMENT OF METALS, AND OTHER SURFACES, WITH DILUTE COLLOIDAL SLIGHTLY ACIDIC DISPERSION OF SILICA. THE METALS BECOME RESISTANT TO CHEMICAL ATTACK.

United States Patent '6 3,796,608 SURFACE TREATMENT Martin B. Pearlman,New York, NY. (78-05 141st St., Flushing, N.Y. 11367) No Drawing.Continuation-impart of application Ser. No. 630,187, Apr. 12, 1967, nowPatent No. 3,578,508. This application May 10, 1971, Ser. No. 141,929

Int. Cl. B23b 15/04 U.S. Cl. 1486.14 6 Claims ABSTRACT OF THE DISCLOSURETreatment of metals, and other surfaces, with dilute colloidal slightlyacidic dispersion of silica. The metals become resistant to chemicalattack.

This application is a continuation-in-part of my application Ser. No.630,187, filed Apr. 12, 1967, now Pat. No. 3,578,508, whose entiredisclosure is incorporated by reference.

In accordance with one aspect of this invention metals are maderesistant to corrosion and to chemical attack by depositing an adsorbedlayer of silica thereon. This may be accomplished by treating theirsurfaces with a dilute slightly acidic colloidal aqueous dispersion ofsilica. Various techniques for making colloidal aqueous dispersions ofsilica are well known in the art. It is convenient to employ dispersionsmade by simply treating finely divided silica (e.g. ground quartz) withwater. The disper sion is preferably quite dilute. Desirably it shouldnot be so concentrated as to yield, on contact with the metal, a depositdistinctly visible to the naked eye.

The metal treatment process of this invention has resulted in theproduction of metallic surfaces which are bright and uncolored and whichseem to the naked eye to be uncoated. Evidently the deposited materialon the metal constitutes at most a very thin and transparent layer muchthinner than 0.001 inch. Hydrophobic surfaces which shed water anddilute sulfuric acid have been produced; this is surprising in view ofthe known hydrophilic nature of silica and it may be due to somecombination with organic material, such as organic hydroxyl compounds(e.g. alcohols such as polyhydric alcohols) that may be present on thesurface of the metal or in the cleaning aids described below; thiscombination may be a physical codeposition on the surface or a chemicalcombination such as an esterification of hydroxyl groups at tached tosilicon atoms.

The metal treated may, for instance, be any of the usual metalsconventionally used for constructing and fabricating articles to 'beexposed to the atmosphere. I have thus far treated ferrous metal (e.g.steel), zinc, aluminum, copper and silver, all with successful results.The striking efiicacy of the process is illustrated by the fact that itmakes zinc resistant to dilute sulfuric acid.

The treated surface may be painted or otherwise coated in conventionalmanner, e.g. painted with the usual oilbased paints such as dryingoil-modified alkyd resin paints, or electroplated with, say, brass,cadmium or chromium.

The metal treatment may also be applied to metals carrying coatings,such as paint or metal plating (e.g. chrome-plating) thereon to furtherprotect the metal, e.g. by depositing the silica or silica-containingmaterial at any of the exposed areas of base metal, such as at pinholesin the coating.

As indicated above, the treating liquid is preferably slightly acidic;generally its pH is above and more usually above 6.

The silica dispersion is preferably applied to a clean metal surface. Inone particularly preferred form of the invention, the silica dispersionis mixed with an aqueous cleaning solution. Particularly suitable is adilute solution made from or containing molasses; for instance, asolution containing the glucose and fructose of blackstrap molasses,preferably together with a surfactant (emulsifying or wetting agent),may be used.

The period of treatment of the metal may be very short. For practicalpurposes periods of less than an hour (e.g. a few minutes or less) arepreferred. The metal need merely be dipped in a bath of the treatingsolution, then removed from the bath and rinsed (as with water) anddried. The temperature of treatment is conveniently from, say, roomtemperature to the atmospheric boiling point of the treating solution,but it is Within the broader scope of the invention to effect treatmentat higher temperatures such as may be obtained under superatmosphericpressures. Temperatures so high as to efi'ect alloying and penetrationof surface material into the body of the metal (as in commercialsiliconizing) are not needed in my process.

The following examples are given to illustrate this invention further.In the examples as in the rest of the application, all proportions areby weight unless otherwise indicated. In the examples, the pressure isatmospheric unless otherwise indicated.

EXAMPLE 1 A colloidal dispersion of silica in water is made by treatingfinely divided highly pure silica flour (of a fineness to pass a 325mesh US. Standard screen) with hot water, in this case water near itsboiling point. This can be done on a small scale by percolating the hotwater through a bed of the silica flour. In one experiment an ordinaryclean 12 cup household coffee percolator is used (the percolator is madeof Pyrex glass, except for the perforated basket which is of aluminumand, for this experiment, is partially covered with filter paper toassist in retaining the silica in the basket. Into the percolator areplaced 16 fluid ounces of water and (in the filter paperlined basket) 25grams of the silica flour. The percolator is heated to cause the waterto boil and to be repeatedly driven up over and through the bed ofsilica flour; this is continued for about 40 minutes. The water becomesturbid (cloudy) and distinctly acidic (pH of 6.03).

The silica flour used above has the following analysis: 99.61% SiO 0.05%ferric oxide, 0.19% alumina, 0.04% titania.

EXAMPLE 2 A particularly suitable cleaning solution for cleaning ofmetal surfaces during the corrosion-proofing treatment is made bydissolving 2. fluid ounces of blackstrap molasses in a quart of Water atabout 120 =F., adding fluid ounce of methanol and allowing the mixtureto stand, e.g., without heating or cooling, in a room at F. for about 5days. During this period a precipitate, believed to be largely sucrose,is formed, owing in part at least to the effect of the methanol; alsothe mixture becomes quite odorous probably due to fermentation. Themixture is filtered (through filter paper) and 10 cc. of 40% formol isadded thereto as a preservative. The resulting dark red brown mixturemay be diluted with water considerably (e.g. a hundredfold) and used toclean metal in conjunction with the silica treatment.

EXAMPLE 3 In a particularly preferred form of the invention the cleaningand treatment are effected simultaneously. To a liter of hot water (atabout F.) there are added 10 cc. of the cloudy liquid of Example 1 and10 cc. of the liquid of Example 2. A piece of rolled mild steel,carrying an oily mill finish is then treated with this mixture byimmersing the steel therein and leaving it there for a short period(e.g. about 1 to 10 minutes, for instance 2 minutes) at roomtemperature. The steel surface is then rinsed immediately with water anddried. To the naked eye the steel surface appears bright like cleansteel but otherwise unchanged by this treatment. However, it is nowhighly resistant to atmospheric corrosion, highly resistant to attack bydilute sulfuric acid (e.g. it may be immersed for days or weeks inaqueous sulfuric acid of, say, to 35% concentration without evidence ofsignificant attack). It is also tested in 3 M HCl solution and is foundto resist attack by that solution. The corrosion resistant surfaceresists abrasion.

EMMPLE 4 Example 3 is repeated except that the metal is aluminum. Themetal appears unchanged to the naked eye but becomes resistant to attackby sulfuric acid, aqueous 4% NaOH solution and aqueous 4% Na COsolution.

EXAMPLE 5 Example 3 is repeated except that the metal is a zinc sheetwhich has been rolled, using oil as the rolling lubricant. The metalappears bright like clean zinc but otherwise unchanged to the naked eyebut becomes resistant to attack by sulfuric acid, aqueous 3 M HCl,aqueous 4% NaOH solution and aqueous 4% Na CO solution.

EXAMPLE 6 Example 3 is repeated except that the metal is copper. Thetreated metal is resistant to attack by sulfuric acid, aqueous 4% NaOHsolution and aqueous 4% Na CO solution.

EXAMPLE 7 A silver-plated table fork (which has been cleaned with silverpolish and washed with soapy water and then rinsed with water and dried)is immersed for about 3 minutes in a mixture of 100 parts of water andone part of the cloudy acidic liquid produced in Example 1, then rinsedwith water and dried. The resulting treated metal retains its silverappearance, is resistant to chemical attack, showing a very greatlyreduced tendency to darken and tarnish on contact with sulfides, eg inuse in contact with eggs or on standing, otherwise unprotected, in theatmosphere.

EXAMPLE 8 Example 1 is repeated using diatomaceous silica (JohnsManville Super-Cel Hyfio) in place of the silica flour. Similar resultsare obtained and the resulting liquid has similar eflects on metals.

EXAMPLE 9 Example 1 is repeated but the silica flour is (a) mixed withthe whole mass of water, in a pot, which is then heated to the boil andmaintained at the boil for /2 hour, or (b) placed on a filter paper in aplastic funnel and leached with the same amount of water (about 30 partsof water per part of silica flour) using water at about roomtemperature; (the liquid passing through the filter is poured over thesilica flour again, repeatedly, and this operation is continued forabout 45 minutes); or (c) mixed with the whole mass of tap water (in aratio of 35 parts of water per part of silica) in a pot, and allowed tostand for 24 hours, at room temperature and then filtered through filterpaper. In each case a white cloudy acidic liquid is obtained, the pHvalues being (a) 6.35 (b) 6.26 and (c) 6.61, each liquid having verygood metal protecting properties when used as in the foregoing examples,although the liquid (c) is not as effective in the treatment.

EXAMPLE 10 50 grams of finely divided silica (crushed quartz) of sizesuch that substantially all of it passes through a 200 mesh sieve ismixed with about 40 ounces of water and the mixture is heated at theboil in air for about 30 min.-

sites (during which about 12 ounces of water evaporates) then cooled andfiltered through filter paper. Suflicient tap water is then added tomake the the volume one quart and the cloudy mixture is stirred in aglass bottle. When tested after about a month of storage, at roomtemperature, its pH is 6.56 and it is found to contain about 0.04 weightpercent of silica.

EXAMPLE 1 1 Another suitable cleaning agent is made by mixing 2 fluidounces of blackstrap molasses and 1 quart of warm water. 3 cc. of 40%formol is added, followed by fluid ounce of a saponin solution (made bybringing to a boil 5 grams of soap bark in one quart of water andcooling). The product is a distinctly acidic liquid.

EXAMPLE 12 fluid ounce of the silica-containing liquid made in Example10 is mixed with the whole product of Example 11, the mixture isfiltered through filter paper (No. 5 Whatman) and diluted with water toraise its pH to about 6.5.

Steel is treated with the resulting mixture, as in Example 3, withsimilar results.

EXAMPLE 13 In this example there is used commercial rolled sheet zincstill carrying the polymeric coating used as a lubricant for rolling.Three strips from the same sheet are used. (a) One strip is directlyplaced into dilute sulfuric acid; gas is evolved and the stripdisintegrates in a short time. (b) The second strip is placed in a bathof a liquid formed by diluting the red brown mixture of Example 2 abouta thousandfold with water, then rinsed with tap water and placed inanother sample of the same dilute sulfuric acid; here, too, gas isevolved and the strip disintegrates in a short time. (c) The third stripis placed for 2 /2 minutes into a bath of a liquid formed by dilutingthe silica-containing liquid of Example 10 about fiftyfold with water,then rinsed with water and placed in another sample of the same dilutesul furic acid; there is substantially no attack on the metal orevolution of gas, but the surface of the metal turns black (which may bedue to an interaction between the sulfuric acid and the polymericcoating).

EXAMPLE 14 Example 11 is repeated, substituting beet sugar molasses(Steffens molasses) for the blackstrap molasses.

Instead of using tap water, or distilled water, for forming the silicadispersion, it is within the broader scope of this invention to use thedilute aqueous solutions (egg. of gallic acid and the other acids orderivatives thereof) that are used (for contact with ores) in said Pat.No. 3,578,508; that is, said solutions are used, in place of the tapwater, to contact the silica.

It is also within the broader scope of this invention to use, in placeof the pure silica, a siliceous mineral containing metal compounds, toform a colloidal silica dispersion similarly containing dispersed ordissolved metal compounds. In this case, as in the application Ser. No.630,187 the metal treated with the aqueous dispersion tends to turncolor, generally assuming the characteristic color of the dispersed ordissolved metal compound.

With respect to the treated metal disclosed in said Pat. No. 3,578,508it has also been found that it lends itself very well to electroplating.In one series of tests, samples thereof were cleaned in an acidiccleaning bath, of the type conventionally used prior to electroplating,and then electroplated under commerical conditions with brass, cadmiumand chromium; in each case the plated sample was foundto be unusuallyresistant to corrosion.

In the examples given herein, all pH measurements are made with a glasscombination electrode and a Beckmann pH meter; when filtering ismentioned it is carried out with Whatman No. 5 filter paper; all sievesizes are U.S. Standard; and all water is New York City tap water whoseanalysis, as supplied by the New York City Department of WaterResources, is given in the following table. Blackstrap molasses,mentioned in the examples, is a well known article of commerce typicallycontaining about 30% sucrose, about 20% reducing sugars and about 20%ash, together with water.

It is understood that the foregoing detailed description is given merelyby way of illustration and that variations may be made therein withoutdeparting from the spirit of the invention. The Abstract" given above ismerely for the convenience of technical searchers and is not to be givenany weight with respect to the scope of the invention.

TABLE Range Average Temperature, F- 33-66 52 Turbidity -8 3 Color (mgJl.1-16 6 Taste and odor 0, Ce, M 0 Nitrogen (mg/1.):

Free ammonia 012-. 084 029 Tctal albuminoid. 04-. 15 10 Nitrite 000-.006 002 Nitrate 20 13 Oxygen consumed (mg 0. 9-2. 5 1. 8 Carbon dioxide(mg./l. 1. 441.6 2.5 Dissolved oxygen (mg/1.). 0-18. 4 14. 8 pH(hydrogen ion cone.) 6. 6-7. 2 6. 9 Bacteria/ml 0. -4 2 Colitorm,percent frequency, ortions /5+. 0. 50 Colitorms, percent samples, 3 5 ormore 0.40 Total organisms (em/ml.) 35-920 220 Amorphous matter(su./m1.).. 275-1, 150 580 Total solids (mg./l.) 38-64 50 Fixed solids(mg-l1.) 21-45 36 Spec. cond. (MMhos 60-71 05 LAS (mg./l.) 00-. 01 01Radiological levels:

Alpha, p.o./l. 00-. 24 08 Beta, .0. 00-11. 3 3. 1 Chloride mg./l 4. 6-5.6 5.3 Alkalinity as CaCOi (mg 5-13 8 Hardness as 0800a In 17-23 19 Ca as08.00: (mg [1 L... 12-16 14 Mg as GaCOi (mg 4-7 5 alcium as 0a. 4. 8-6.45. 6 as Mg- .90-1.7 1.4 Carbonate (m ./l.)- .00 .00 Cyanide (mg. .000-.007 002 Fluoride (mg/1. .05-1. 25 87 de (mg [1.) 001 05-. 22 i3 1.0-3 02.6 9.5-13 5 11.8 .00-. 05 02 000-. 001 001 .04-.06 .05 00-. 04 .01 00-.00 00 Oil-.00 00 02-. 08 05 .03-. 25 .06 a Mercury mg. Po m (mg./l.)..0.5-1.00 .62

What is claimed is:

1. Process for treating metal surfaces to improve their resistance tochemical attack which comprises bringing said surfaces into contact withan aqueous acidic composition consisting essentially of a colloidaldispersion of silica, a water-soluble sugar and a surfactant, andremoving said metal surface from contact with said composition beforeany deposit of silica visible to the naked eye is formed on saidsurface, and metal being ferrous metal, zinc, aluminum, copper orsilver.

2. Process as in claim 1 in which said silica is dispersed by contactingfinely divided silica of less than 200 mesh particle size with water.

3. Process as in claim 1 in which the period of said contact is lessthan one hour and the concentration of silica in said composition is upto about 0.4 weight percent.

4. Process as in claim 1 in which said sugar is molasses.

5. Process as in claim 4 in which said surfactant is saponin.

6. Product of the process of claim 1.

References Cited UNITED STATES PATENTS 3,013,897 12/1961 Cupery et al.117-1351 3,133,829 5/1964 Cupery et al. 117-135.1 3,320,082 5/1967McMahon et al. 117-l35.1 2,787,967 4/1957 Nohejl l17135.1 3,506,4994/1970 Okada et al. 117--135.1 1,948,029 2/19'34 Fisher 252396 2,978,3494/1961 Walsh et al. 106287 S 3,108,970 10/1963 Luvisi 252-309 3,249,5475/ 1966 Fisher 252-396 OTHER REFERENCES V. E. Skipalev. Extraction ofSugar From Feed Molasses. In Chemical Abstracts. 55 (7) :6896h, Apr. 3,1961.

CAMERON K. WEIFFENBACH, Primary Examiner US. Cl. X.R.

